Sensor system and method for web manufacturing

ABSTRACT

The present invention provides a sensing system and method adapted for use in monitoring and detecting features of a web for manufacturing. The sensing system has an energy source adapted to project an energy beam onto the web and a sensor positioned relative to the web and the energy source to sense attenuation of the energy beam from the energy source to detect, locate, identify, or measure the web or its features. The method includes passing the web through a light from a light source, measuring attenuation of the light from the light source with an optical sensor, and identifying an optical signature as a function of attenuation for characterizing the web and/or its feature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §120 to provisionalapplication Ser. No. 60/980,318 filed Oct. 16, 2007, herein incorporatedby reference in its entirety.

BACKGROUND

The present invention relates to articles of manufacture prepared from amaterial web, and in particular to the manufacture of plastic bag rollssuitable for use in most application, including for example, trash canliners, produce bags, and the like. Plastic bag rolls are typicallybuilt by continuously extruding plastic film through a die to form abubble. The bubble, tubular in shape, is later reduced in width to thatof the desired bag by flattening the shape and introducing folds knownas gussets using rollers. Once flat, the web may be printed beforeconversion into bags. Timing marks may be incorporated into the print.

Two types of machines are usually involved in the final step, known asconversion. The first machine, commonly referred to as the ‘bagmachine,’ perforates and seals the bag web at intervals that determinethe length of the final bag. The seals and perforation are approximatelyperpendicular to the web. The second machine, commonly known as the‘winder,’ separates the web at the perforation if an overlapped bag isbeing built but always winds the web into a roll while counting thebags. The ‘winder’ automatically transfers a new spindle into the web tocontinue winding bags when a roll has been completed.

Because the perforation is introduced onto the web in a differentmachine than the machine that winds the roll, the ‘winder’ mustsynchronize its operation to the location of the perforation and seal.The device used to determine the location of the perforation on the webis referred to as the ‘counter.’ The most prevalent form of counter is aperforation spark gap detector. This design incorporates two electrodesat a high voltage potential, one on each side of the web, at closeproximity. When the plastic bag is between the electrodes, it acts as aninsulator. However, when the perforation section passes the electrodes,the insulator is compromised and a spark can jump the gap between theelectrodes. Such a design is not always satisfactory, as the highvoltage used for sensing also induces a static bond between the layersof the plastic bag. This effect increases the difficulty that a personwill have in opening the bag. Furthermore, the presence of an exposedhigh voltage device on the input of the winding machine often causesoperator shocks. Moreover, the sensor can only detect the perforation,and not any other features of the bag and/or plastic bag web.

Therefore, a need in the art has been identified to provide a sensorsystem to identify, track, locate, and/or measure features associatedwith a plastic bag web, such as bag seals, perforations, printedmarkings, skirt length, or other features on the plastic roll, bag orbag web.

SUMMARY OF THE INVENTION

These particular objects and advantages may apply to only someembodiments falling within the claims and thus do not define the scopeof the invention. In one aspect of the present invention a sensingsystem adapted for use in monitoring and detecting features of a web formanufacturing is disclosed. The sensing system includes an energy sourceadapted to project an energy beam onto the web and a sensor positionedrelative to the web and the energy source to sense attenuation of theenergy beam from the energy source to detect, locate or measure the webor features of the web. In a preferred form, the energy source is alight source and the energy beam is a light beam. The energy source ispositioned on one side of the web and the sensor is aligned with theenergy source on an opposite side of the web so that the web passesbetween the energy source and the sensor. In a preferred form, at leasta portion of the energy beam is transmitted through the web so that theportion of the energy beam passing through the web is sensed by thesensor. The sensing system also includes a comparator in datacommunication with the sensor to measure a difference in energy betweenthe energy beam and the portion of the energy beam that passes throughthe web. The sensing system identifies the difference as energysignatures for the web and/or a feature of the web, which may includebut are not limited to: a) a perforation of the web; b) a seal of theweb; c) a timing mark of the web; d) a skirt length of the web; or e)any part or dimension of the web ascertainable by measuring attenuationof the energy beam.

In another aspect of the present invention, a plastic bag manufacturingmachine adapted to detect the existence and/or location of one or morefeatures in the bag is disclosed. The machine includes a machine framewith one or more components for supporting and handling a plastic bagweb, an energy source on the machine proximate the plastic bag web toproject an energy beam onto the plastic bag web, and a sensor on themachine proximate the plastic bag web and the energy source to senseattenuation of the energy beam projected onto the plastic bag web fromthe energy source. In a preferred form, the energy source is a lightsource, the energy beam is a light beam and the light source isadjustable in intensity or frequency to be tuned to each specificplastic bag web or to filter out background light. The energy source maybe positioned on the machine on one side of the plastic bag web and thesensor aligned with the energy source on the machine on an opposite sideof the plastic bag web to sense at least a portion of the energy beampassing through the plastic bag web, or the energy source and the sensormay be positioned on the machine on one side of the plastic bag web sothat the sensor is positioned relative the energy source and the plasticbag web on the machine on the one side to sense at least a portion ofthe energy beam reflected off of the plastic bag web.

A method of the present invention for detecting and measuring one ormore features of a bag web is also disclosed. The method includes thesteps of passing the bag web through a light from a light source,measuring attenuation of the light from the light source with an opticalsensor, and identifying an optical signature as a function ofattenuation for characterizing the bag web and/or its features. In apreferred form, the method includes the steps of: a) acquiring theoptical signature from the optical sensor with a controller forcomparing with a record describing what optical signatures should havebeen acquired; and, b) associating the line speed of the bag web withthe record of detections for each optical signature for: i) confirmingthe presence of each feature of the bag web, ii) measuring one or moreof the features of the bag web, and/or iii) determining false/positivereadings from the optical sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a front elevation view of a plastic bag manufacturing machineof the prior art with the sensing system of the present invention.

FIG. 2 is a top view of the plastic bag web taken along line 2-2 in FIG.1

FIG. 3A is a side view of the plastic bag web taken along line 3A-3A inFIG. 1.

FIG. 3B is another exemplary embodiment of the sensing system of thepresent invention shown in FIG. 3A.

FIG. 4 is a simplified electrical block diagram of the sensor systemaccording to an exemplary embodiment of the present invention.

FIG. 5 is a flow chart of the feature detection function of the sensorsystem according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The present invention is directed towards a sensing system and methodadapted for use in manufacturing bags from a bag web and for use indetecting features associated with the bag or bag web.

Referring now to FIG. 1, a plastic bag manufacturing machine 10 of thekind that is commercially available is shown by way of example. Thoseskilled in the art can appreciate that plastic bag manufacturing machinecould be a paper, plastic, metal or any other web type manufacturingmachine. The plastic bag manufacturing machine 10 could be a bagmachine, a winder, a counter as discussed in the Background or any othermachine for manufacturing plastic bags suitable for adaptation with thesensing system 20 of the present invention. The present invention shouldnot be construed as being limited to plastic bag manufacturing machinesonly. The present invention contemplates that sensing system 20 could beused to monitor, detect, or measure features in other bag webs formanufacturing products where detection by attenuation of an energy beamis plausible, such as for example bag webs of materials suitable fordetecting, measuring, locating, or monitoring features of the bag web byattenuation of an energy beam transmitted or reflected off the web. Theplastic bag manufacturing machine 10 of the prior art includes a frame12 for supporting one or more rollers 14 or other components forhandling, supporting and shuttling the plastic bag web 16 through themachine. The plastic bag web 16 may be unrolled from a plastic bag roll,such as bag roll 18, or received from another bag manufacturing machinein communication with or tied to plastic bag manufacturing machine 10.The plastic bag manufacturing machine 10 may include controls 24 foroperating, controlling and monitoring machine 10. The plastic bagmanufacturing machine 10 may also be operated by being linked up by wireor wirelessly with computer 22. Those skilled in the art can appreciatethat computer 22 could be any programmable or other controller unit,such as a programmable logic controller (PLC). The controller mayinclude a data store. Computer 22 could be in data communication withplastic bag manufacturing machine 10 to monitor operating parameters ofmachine 10 such as line speed of the plastic bag web 16. Computer 22 mayalso be in data communication with sensing system 20 for monitoring,controlling or tuning sensing system 20. The computer 22 oralternatively a controller with a data store could receive and storeinformation, such as readings from sensor 36 (shown in FIG. 3A-B and 4).The computer 22 or alternatively a controller could also be used tocontrol operation of sensing system 20.

Referring now to FIG. 2, a plastic bag web 16 that contains a seal 26and perforation 28, and optionally a printed mark 30 is shown by way ofexample. Other optically detectable (or detectable by energyattenuation) and/or notable features of the plastic bag web 16 includeskirt length and other like dimensions valuable in ascertaininginformation about the plastic bag web 16 or plastic bag duringmanufacturing, handling, packaging or the like. Plastic bag web 16 orplastic bags, like the type illustrated in FIG. 2, are generallymanufactured in commercially available machines, such as the machineshown in FIG. 1. The bags manufactured by these machines have a widevariety of uses, including, for example, trash can liners, and producebags and other like uses for storage or disposal.

Plastic bag rolls or plastic bag webs 16 are typically constructed bycontinuously extruding plastic film through a die to form a bubble. Thebubble, tubular in shape, is later reduced in width to that of thedesired bag by flattening the shape and introducing folds known asgussets using rollers. Once flat, the plastic bag web 16 may be printedon before conversion into bags. Timing marks may be incorporated intothe print. In the final stages of manufacturing the bag, a machine,referred to as a “bag machine,” perforates and seals the plastic bag web16 at intervals that determine the length of the final bag. Othermachines such as a “winder” may separate the plastic bag web 16 at theperforation if an overlap bag is being built, but ultimately, the“winder” winds the plastic bag web 16 into a roll while counting thebags. The winder may be adapted to automatically transfer a new spindleinto the plastic bag web 16 to continue winding bags when a roll iscomplete.

Because the perforation 28 is introduced into the plastic bag web 16 ina different machine than the machine that winds the roll, the winder isadapted to synchronize the operation to the location of the perforation28 and the seal 26 on the plastic bag web 16. The device used todetermine the location of the perforation 28 on the plastic bag web 16is often referred to as “counter.” In the prior art, these counterscommonly consist of a perforation spark gap detector. Spark gapdetection incorporates two electrodes at a high-voltage potential, oneon each side of the bagging, at close proximity. When the plastic bagweb 16 is between electrodes, it acts as an insulator. However, when theperforation section passes the electrodes, the insulator is compromisedand a spark can jump the gap between the electrodes, which is trackedand identified to determine the location of the perforation on theplastic bag web. As discussed in the background, such a design is notalways satisfactory, as high-voltage use for sensing also induces astatic bond between the layers of the plastic bag. This effect increasesthe difficulty that a person will have in opening the bag. Furthermore,the presence of an exposed high-voltage device on the input of thewinding machine often results in operator shocks. Further, the sensorcan only detect the perforation 28 and not any other feature associatedwith the plastic bag web 16. Because the prior art has these and otherlimitations, the sensing system 20 of the present invention has beenprovided to identify, track, locate, and measure features associatedwith the plastic bag web 16, such as bag seals 26, perforations 28,printed markings 30, or other features on the plastic bag web 16, whichmay be identifiable, measurable, locatable, and/or detectable bymeasuring attenuation of an energy beam transmitted through or reflectedoff of the material used for the bag web, such as plastic bag web 16.

One exemplary embodiment of the optical sensor is shown in FIG. 3A. Thesensing system 20 and methods of the present invention may include oneor more energy sources 32, such as a light source or any other sourcecapable of emitting energy beam 34, and one or more sensors 36, such asan optical sensor, aligned with energy source 32, energy beam 34 andrelative to the plastic bag web 16 such that one or more opticallyidentifiable features (or features identifiable by attenuation of anenergy signal) in the plastic bag web 16 may be detected, measured, orpositionally identified. In one exemplary aspect of the presentinvention, plastic bag web 16 may be passed between the aligned energysource 32 and sensor 36 as illustrated in FIG. 3A, whereby an energybeam 34, such as a light beam, from energy source 32 is attenuated as itpasses through the plastic bag web 16. The amount of attenuation may bedetected at the sensor 36, such as an optical sensor/detector in thecase where the energy source 32 is emitting light. Thus, by attenuationof energy beam 34 from energy source 32 passing through the plastic bagweb 16, the sensor 36 is able to identify energy signatures associatedwith each of the features of the plastic bag web 16. For example, in thecase where the energy source 32 is a light source, attenuation of lightfrom the light source passing through the plastic bag web 16, iscaptured by an optical detector, which associates an optical signaturewith each of the features of the plastic bag web 16, such as the seal26, perforation 28, printed mark 30, or other optically identifiablefeatures of the plastic bag web 16. Each of these features and otheroptically identifiable features of the plastic bag web 16 are opticallyidentifiable because they each possess different optical characteristicsfrom each other and the rest of the plastic bag web 16. Using thedifferences in optical characteristics of these features, theirrespective locations and measurements may be derived. For example,knowing the line speed of the plastic bag web 16, sensing system 20could deduct the measurements of one or more features of the plastic bagweb by comparing the time between detections with the line speed of theplastic bag web 16. This could be accomplished using a detectionalgorithm operating as part of the sensing system or computer 22. In thecase where the energy source emits light, the attenuation of light fromthe energy source 32, as previously discussed, may be detected ormeasured using a sensor 36, such as an optical detector. The opticaldetector may include a phototransistor, photodiode or like devicesuitable for measuring attenuation of light source and/or determining anoptical signature (as a function of attenuation) for each featureassociated with the plastic bag web 16.

Another exemplary embodiment of the sensing system 20 and methods areillustrated in FIG. 3B. In this embodiment, the energy source 32 andsensor 36 are aligned and positioned with respect to the plastic bag web16 so as to measure or detect variation or attenuation in the energybeam 34 reflected off of the plastic bag web 16 and/or features of theplastic bag web 16. For example, in the case where the energy source 32is a light source and the sensor 36 is an optical sensor, the two may bealigned and positioned with respect to the plastic bag web 16 so as tomeasure or detect variances or attenuation in the light to detectchanges in the optical characteristics of the plastic bag web 1 usingreflective light as an optional detection scheme. In this example, theoptical detector/sensor may be positioned relative to the plastic bagweb 16 and the light source so that reflected light from the plastic bagweb 16 may be detected and attenuation of the reflected light measured(compare the reflected light to the emitted light) to distinguishspecific features of the plastic bag web 16 from the rest of the plasticbag web 16.

The present system and methods contemplate other options for identifyingthe plastic bag web 16 and features of the plastic bag web 16. In oneaspect of the present invention, features of the plastic bag web 16 maybe identified, located, and measured by comparing the measured energybeam 34 or light to a set point or previously measured light level, suchas emitted energy or light levels, that are correlated to or associatedwith each of the specific features of the plastic bag web 16, such asthe perforation 28, seal 26, printed mark 30, skirt length (the distancebetween perforation 28 and seal 26), or other features of the plasticbag web 16 identifiable by attenuation of energy beam 34, such asoptically identifiable features. In another aspect of the presentinvention, sensing system 20 may be adapted such that the electricalresponse of the optical sensor may be compared to a threshold responseknown to represent the overall plastic bag web 16 response to determineif a seal 26, perforation 28, printed mark 30, or other bag features arepositioned at the detection aperture between the detector and lightsource. Furthermore, a baseline response for the plastic bag web 16 maybe generated and compared with the response received from each of thefeatures of the plastic bag web 16 when light from the light source isattenuated by transmission or reflection from the various features onthe plastic bag web 16. The comparison algorithm for comparing emittedand measured light could be part of sensing system 20 and/or computer 22(shown in FIG. 1). In other aspects of the present invention, sensor 36may have features for internal regulation of the frequency and intensityof the energy source 32, such as the light source, so that it can betuned to a particular plastic bag web 16 or to filter out backgroundlight radiation. Computer 22 or a controller in communication withsensing system 20 may also be used to tune the light source to eachspecific plastic bag web 16 and/or the background light by comparingemitted and measured light readings. In the case where the energy source32 is a light source, light emitted from the light source may also beadjustable in intensity or frequency. 4. The sensing system 20 may alsobe configured to maintain a historical record of detections versus time,line speed of plastic bag manufacturing machine 10 or other parameterssuch that various bag characteristics or features can be determined,measured, located, or identified. The sensing system 20 may include acontroller and data store for processing and storing detectioninformation or operating cooperatively with computer 22. The sensingsystem 20 may also be adapted to use this historical record tosubstitute missing detection information at the correct intervals, ifnecessary.

FIG. 4 illustrates an exemplary electrical schematic of energy source32, sensor 36, and controller 46. Energy source 32 may include, but isnot limited to, a regulator 38 that is adapted to convert the availablepower to a suitable form for the energy source 32 whereby the intensity,frequency, or other parameters of the energy source 32 may be controlledand tuned specifically to the plastic bag web 16 by controller 46 incommunication with regulator 38. In another aspect, as also illustratedin FIG. 4 relating to sensor 36, the measured signal from detector 38may be amplified with amplifier 42 and ultimately compared or correlatedto one or more thresholds associated with the plastic bag web 16 incomparator 44. The signal may be converted from an analog signal to adigital signal at any point to optimize processing of data from thedetector 40, whether processed in real-time or post-processed withprocessing algorithms on computer 22 or a controller with a data storeas part of the sensing system 11. The regulator 38, energy source 32,detector 40, amplifier 42, and comparator 44 may be operated by computer22, a controller or a CPU having a control board and programmed withcode as shown in the FIG. 5 for operating the detection function of thesensing system 20. Using computer 22 or a controller with a data storenot shown, detection data may be collected from the detector 40, such assignal levels or otherwise, time-stamped or otherwise, to performanalysis of the signaled response. Signal thresholds may be determinedusing the comparator 44. Comparator 44 may be configured to assessstatistical methodologies programmed in the computer 22 or a controllerto determine the average response of the detector 40, to furtheridentify false/positives detections, and/or supply information tocontroller 46 for operating the sensing system 20 and/or operationalparameters of the plastic bag manufacturing machine 10. Signal responselevels having a time signature and carrying embedded line speedinformation reported by the plastic bag manufacturing machine 10 tocomputer 22 may be used to measure dimensional parameters of the plasticbag web 16, such as length of the bag, seal 26, perforation 28, printedmarks 30, or other optically detectable, measurable, or identifiablefeatures of the plastic bag web 16.

Methods of the invention are also disclosed according to one or moreexemplary embodiments. FIG. 5 illustrates a flow chart method for thefeatured detection function of the sensor system 20 of the presentinvention. In one exemplary aspect of the present invention, sensingsystem 20 is configured for detecting and measuring one or more featuresof plastic bag web 16 for manufacturing plastic bags. Those skilled inthe art can appreciate that the sensing system 20 of the presentinvention could be used to measure, detect, identify and/or monitorfeatures associated with any web used in manufacturing, such as aplastic, paper or metal web. The method includes one or more of thesteps of passing the plastic bag web 16 through an energy beam 34, suchas light, from an energy source 32, such as a light source, formeasuring attenuation of energy beam 34 from the energy source 32 with asensor 36. The method also includes identifying an energy signature,such as an optical signature, as a function of the resulting attenuationfor characterizing the plastic bag web 16 and/or any of its features.

As previously indicated, the methods of the present invention are notlimited to monitoring, identifying, and/or detecting features associatedwith the plastic bag web 16, but the methods of the present inventioncould be used to monitor, detect and/or measure features associated withany web of material, whether plastic, metal or paper webs used in amanufacturing process that use a web of material. For example, thefigures such as FIG. 5 illustrate one exemplary method of the detectionfunction of the present invention or the function for detecting,monitoring and/or measuring features associated with the web 16 used inmanufacturing. The detection function could be started by a userinputting operating parameters such as selecting the type of material ofthe web 16 or the type of product to make from the web 16, such as aplastic bag. Based on these selections, operational parameters of thesensing system 20 are formulated and can be executed by computer 22 orany type of controller, such as a micro-controller in communication withan I/O device that in-turn is in communication with other externalhardware structures such as energy source 32, energy beam 34, sensor 36,regulator 38, detector 40, amplifier 42, comparator 44, and/orcontroller 46 (as shown in FIG. 4).

Upon operation startup, sensing system 20 may acquire an initialtimestamp, which could be used as a reference point in the detectingprocess, such as for example providing information based on the positionof the web 16 and/or features in web 16, relative to the referencepoint. A second timestamp is taken upon the start of perforation 28 inplastic bag web 16. In the case where the start of a perforation 28 isnot detected during the expected interval, thereby causing theperforation interval to expire, sensing system 20 checks to see ifsensor 36 changed state, and if not provides a no detection warning. Ifthe time interval for detecting perforation 28 has not expired, sensingsystem 20 checks to see if the sensor 36 has changed state. If sensor 36has not changed state, sensing system 20 cycles again until a secondtimestamp is acquired upon the detection of the start of perforation 28.However, if sensor 36 changes state (i.e., an energy signal is detectedin excess of the standard response for web 16) then sensing system 20acquires a third timestamp indicating the end of perforation 28 inplastic bag web 16. In the case where the bounce interval doesn't expire(i.e., interval of time that the signal response is what the expectedresponse should be for the feature in question) the system checks to seeif sensor 36 has changed state, and if not repeats the process untileither the bounce interval expires or sensor 36 changes state(indicating a detection of the end of perforation 28). In the case wherethe bounce interval has not expired, but sensor 36 has changed state(i.e., a third timestamp has been acquired for the end of perforation28), sensing system 20 automatically increments the perforation bouncecounter.

Alternatively, in the case where the bounce interval has expired (i.e.,sensor 36 changed state and bounce counter was incremented), sensingsystem 20 acquires a fourth timestamp of the starting point for seal 26in plastic bag web 16. In the case where the seal 26 interval (timeallotted for detection of the seal) expires, meaning that no seal 26 wasdetected and sensor 36 did not change state, sensing system 20 attemptsto reacquire the start of seal 26. If the start of seal 26 is detected,sensor 36 changes state and a fifth timestamp is acquired at the end ofseal 26. In the case where the interval for detecting seal 26 expires,without a acquiring a fourth timestamp for the start of the seal 26,sensing system 20 increments the counter for the no seal counter. If thedetection interval for seal 26 has not expired and sensor 36 has changedstate, the sensing system 20 continues to cycle until the start of seal26 is detected.

Sensing system 20 attempts to acquire a fifth timestamp at the end ofseal 26. In the case where the bounce interval doesn't expire (i.e.,interval of time that the signal response is what the expected responseshould be for the feature in question) and sensor 36 has not changedstate, sensing system continues to cycle until sensor 36 changes stateindicating a detection of the end of seal 26. In the case where thebounce interval has not expired and sensor 36 has changed state, sensingsystem 20 automatically acquires the fifth timestamp for the end of seal26 and increments the seal bounce counter.

Alternatively, in the case where the bounce interval expired (i.e.,sensor 36 changed state and bounce counter was incremented), sensingsystem 20 applies timing delays and provides an output pulse whichincrements the bag counter, which could be alternatively resetexternally. In the case where the seal was detected, the system 20 usesthe information to determine and perform statistical analysis, whetherby real time or post processing, to determine dimensions, locations,and/or detection of the skirt length, seal length or seal bounces forplastic bag web 16. Alternatively, and in addition to the previous step,in the case where seal 26 was not detected, sensing system 20 can beused to determine other features associated with plastic bag web 16 suchas perforation length, perforation bounces, perforation ratio, and/orbag length.

The embodiments of the present invention have been set forth in thedrawings and specification and although specific terms are employed,these are used in the generically descriptive sense only and are notused for the purposes of limitation. Changes in the form and proportionof parts as well as in substitution of equivalents are contemplated ascircumstances may suggest or are rendered expedient without departingfrom the spirit and scope of the invention as further defined in thefollowing claims.

1. A sensing system adapted for use in monitoring and detecting featuresof a web for manufacturing, the sensing system comprising: an energysource adapted to project an energy beam onto the web; and a sensorpositioned relative to the web and the energy source to senseattenuation of the energy beam from the energy source to detect, locateor measure the web and/or features of the web.
 2. The sensing system ofclaim 1 wherein the energy source comprises a light source and theenergy beam comprises a light beam.
 3. The sensing system of claim 1wherein the energy source is positioned on one side of the web and thesensor is aligned with the energy source on an opposite side of the web,the web passing between the energy source and the sensor.
 4. The sensingsystem of claim 3 wherein at least a portion of the energy beam istransmitted through the web, the portion of the energy beam passingthrough the web is sensed by the sensor.
 5. The sensing system of claim4 further comprising a comparator in data communication with the sensorto measure a difference in energy between the energy beam and theportion of the energy beam that passes through the web.
 6. The sensingsystem of claim 5 wherein the difference comprises an energy signaturefor the web and/or a feature of the web.
 7. The sensing system of claim6 wherein the feature comprises: a) a perforation of the web; b) a sealof the web; c) a timing mark of the web; d) a skirt length of the web;or e) any part, alteration or dimension of the plastic bag webascertainable by measuring attenuation of the energy beam.
 8. Thesensing system of claim 1 wherein the energy source and the sensor arepositioned on one side of the web, the sensor positioned relative theenergy source and the web on the one side to sense at least a portion ofthe energy beam reflected off of the web.
 9. The sensing system of claim1 in combination with a machine for manufacturing plastic bags.
 10. Thesensing system of claim 1 in combination with a plastic bag windingmachine.
 11. The sensing system of claim 1 in combination with a plasticbag counter machine.
 12. The sensing system of claim 1 wherein the webcomprises: a) a paper web; b) a plastic web; or c) a metal web.
 13. Aplastic bag manufacturing machine adapted to detect the existence and/orlocation of one or more features in the bag, the machine comprising: amachine frame with one or more components for supporting and handling aplastic bag web; an energy source on the machine proximate the plasticbag web to project an energy beam onto the plastic bag web; and a sensoron the machine proximate the plastic bag web and the energy source tosense attenuation of the energy beam projected onto the plastic bag webfrom the energy source.
 14. The machine of claim 13 wherein the energysource comprises a light source and the energy beam comprises a lightbeam.
 15. The machine of claim 14 wherein the light source is adjustablein intensity or frequency to be tuned each specific plastic bag web orto filter out background light.
 16. The machine of claim 13 wherein: a)the energy source is positioned on the machine on one side of theplastic bag web and the sensor is aligned with the energy source on themachine on an opposite side of the plastic bag web to sense at least aportion of the energy beam passing through the plastic bag web; or b)the energy source and the sensor are positioned on the machine on oneside of the plastic bag web, the sensor positioned relative the energysource and the plastic bag web on the machine on the one side to senseat least a portion of the energy beam reflected off of the plastic bagweb.
 17. The machine of claim 13 further comprising a comparator tomeasure an energy difference between the energy beam and the portion ofthe energy beam reflected off of and/or transmitted through the plasticbag web.
 18. The machine of claim 17 wherein the energy differencecomprises a signature for the plastic bag web and/or a feature of theplastic bag web.
 19. The machine of claim 18 wherein the featurecomprises: a) a perforation of the plastic bag web; b) a seal of theplastic bag web; c) a timing mark of the plastic bag web; d) a skirtlength of the plastic bag web; or e) any part or dimension of theplastic bag web ascertainable by measuring attenuation of the energybeam.
 20. A sensing system for use in manufacturing plastic bags from aplastic bag web and adapted to detect the existence and/or location ofone or more features of the bag and/or bag web, the sensing systemcomprising: a light source adapted to project a light onto the plasticbag web; an optical sensor positioned relative to the plastic bag weband the light source to sense attenuation of the light from the lightsource by transmittance or reflectance; and a comparator incommunication with the optical sensor and the light source to measureattenuation of the light transmitted through or reflected off of theplastic bag web to provide an optical signature for the bag and/or oneor more features of the plastic bag web.
 21. The sensing system of claim20 wherein the comparator comprises a phototransistor, photodiode orlike device adapted to produce an electrical response for each opticalsignature associated with the bag and/or the features of the plastic bagweb.
 22. The sensing system of claim 20 further comprising a controllerhaving a data store in communication with the comparator for storingdata relating to the existence and/or location of the features of thebag and/or plastic bag web.
 23. The sensing system of claim 22 whereinthe controller is in communication with the sensor to detect, store,calculate, respond to, and prepare a history of attenuation versus timeof attenuated light readings.
 24. A method for detecting, monitoring andmeasuring one or more features of a plastic bag web for manufacturingplastic bags, the method comprising: mounting an energy source and asensor proximate each other and a plastic bag web on a machine formanufacturing plastic bags; sensing a level of attenuation of an energybeam from the energy source transmitted through or reflected off of theplastic bag web and/or one or more features of the plastic bag web; andassociating the level of attenuation with each feature and/or theplastic bag web for monitoring, measuring and detecting the presence ofeach feature and/or the plastic bag web during manufacturing.
 25. Themethod of claim 24 further comprising the step of tuning frequency andintensity of the energy source to each plastic bag web.
 26. The methodof claim 24 further comprising the step of creating a time record foreach time the feature is detected for post-processing detections for theplastic bag web and/or the one or more features.
 27. The method of claim24 further comprising the step of measuring an energy signal for the oneor more features comprising: a) a perforation of the plastic bag web; b)a seal of the plastic bag web; c) a timing mark of the plastic bag web;d) a skirt length of the plastic bag web; or e) any part or dimension ofthe plastic bag web ascertainable by measuring attenuation of the energybeam.
 28. The method of claim 26 further comprising the step ofsubstituting a missing detection for one of the features at a correctinterval using the time record.
 29. The method of claim 24 furthercomprising the step of characterizing the level of attenuation for eachfeature by comparing to a baseline level of attenuation for the plasticbag web.
 30. A method for detecting and measuring one or more featuresof a bag web, the method comprising: passing the bag web through a lightfrom a light source; measuring attenuation of the light from the lightsource with an optical sensor; and identifying an optical signature as afunction of attenuation for characterizing the bag web and/or eachfeature of the bag web.
 31. The method of claim 30 further comprisingthe step of acquiring the optical signature from the optical sensor witha controller for comparing with a record describing what opticalsignatures should have been acquired.
 32. The method of claim 31 furthercomprising the step of associating the line speed of the bag web withthe record of detections for each optical signature for: a) confirmingthe presence of each feature of the bag web; b) measuring one or more ofthe features of the bag web; and/or c) determining false/positivereadings from the optical sensor.